The objective of the proposed research is to gain insight into the control of gene expression, particularly during embryogenesis. We are examining the synthesis, processing and turnover of a number of specific mRNAs in cultured Drosophila cells. These include two abundant mRNAs and a heat shock mRNA. We are examining transcription in the embryos by redering them permeable with octane, then labeling with 3H uridine. The transcription of specific genes (ribosomal and histone), is being examined using cloned DNA sequences as probes. The total newly synthesized mRNA is being studied by in situ hybridization to polytene chromosomes. We are also attempting to localize specific mRNA sequences in the embryo by in situ hybridization of 3H cRNA from cloned sequences to histological sections.